Oakum — originally: the coarse woody fibres (hurds or tow) separated from the finer fibres of flax or hemp; (also) clippings, trimmings, shreds (obs.). Later (also): esp. loosely twisted fibres obtained chiefly by untwisting and picking old hemp rope; such fibres or the like, used as a caulking material for the seams of wooden ships, the joints of pipes, etc., and formerly sometimes in dressing wounds. OED (1989).